Piston for an internal combustion engine

ABSTRACT

The invention relates to a piston ( 10, 110, 210 ) for an internal combustion engine, comprising a piston head ( 11, 111, 211 ) and a piston skirt, the piston head ( 11, 111, 211 ) having a circumferential ring section ( 15, 115, 215 ) and a circumferential cooling channel ( 16, 116, 216 ) in the region of the ring section ( 15, 115, 215 ). The cooling channel has a cooling channel floor ( 17, 117, 217 ) and a cooling channel ceiling ( 18, 118, 218 ). According to the invention, the cooling channel ( 16, 116, 216 ) has a narrowing ( 20, 120, 220 ).

The present invention relates to a piston for an internal combustionengine, having a piston head and a piston skirt, wherein the piston headhas a circumferential ring belt as well as a circumferential coolingchannel in the region of the ring belt, and the piston skirt has aworking surface assigned to its major thrust side and a working surfaceassigned to its minor thrust side.

Pistons of the stated type are exposed to great mechanical andparticularly thermal stresses in modern internal combustion engines. Forthis reason, there is a fundamental need for constantly optimizing thecooling of the pistons, by means of feeding coolant into the coolingchannel, particularly in the region of the piston crown.

The task of the present invention consists in further developing apiston of the stated type in such a manner that cooling is furtherimproved in the region of the piston crown.

The solution consists in that the cooling channel has a narrowing.

The present invention is based on the continuity equation of fluiddynamics, according to which narrowing of the flow cross-section leadsto an increase in the flow velocity in flowing fluids. In the pistonaccording to the invention, the narrowing provided according to theinvention, in interaction with the Shaker effect, brings about theresult that coolant circulating in the cooling channel is not onlythoroughly mixed, but also accelerated in targeted manner by means ofthe narrowing, and guided in the direction of the piston crown. Thisbrings about the result that the thoroughly mixed and thereby cooledcoolant is moved past the particularly hot wall sections of the coolingchannel in the region of the piston crown significantly more efficientlyand frequently per piston stroke than in the previously known pistons.Therefore the heat transfer coefficient between cooling channel wall andcoolant is increased, and thereby the cooling of the piston according tothe invention is significantly improved.

Advantageous further developments are evident from the dependent claims.

It is practical if the narrowing provided according to the invention hasa distance from the cooling channel floor that corresponds to at leastone-third of the axial height and/or at most two-thirds of the axialheight of the cooling channel. In this way, particularly effectiveacceleration of the coolant stream in the direction of the coolingchannel ceiling can be achieved. To optimize the acceleration, thenarrowing preferably has essentially the same distance from the coolingchannel floor and from the cooling channel ceiling.

It is practical if the narrowing is configured as a circumferentialnarrowing, in order to bring the acceleration effect about along theentire cooling channel.

A preferred further development provides that the narrowing is formed bymeans of precisely one material elevation on a cooling channel wall, andthat the cooling channel ceiling is configured essentially in domeshape. With this, the result is achieved that the coolant is forced intoa flow that circulates in circular shape, in the region of the coolingchannel ceiling, so that interacts with the wall of the cooling channelmultiple times per piston stroke. In this connection, coolant at a lowertemperature is always accelerated and additionally delivered by thenarrowing. This effect is particularly effective if the radial dimensionof the essentially dome-shaped cooling channel ceiling, at its widestpoint, is at least equal to twice the radial dimension of the narrowing.In this case, coolant that is less hot can flow downward, so that theflow of coolant at a lower temperature through the narrowing, in thedirection of the cooling channel ceiling, is not significantly hindered.

A further preferred embodiment of the present invention consists in thatthe narrowing is formed by means of two material elevations that lieopposite one another on two cooling channel walls. This embodiment isparticularly suitable in the case of multi-part friction-welded pistons,if the weld seam runs through the cooling channel, so that the weldbeads form the material elevations that lie opposite one another andbring about the narrowing.

In this embodiment, it is particularly advantageous if the coolingchannel ceiling has a flow divider at its zenith, which divider isdisposed centered relative to the narrowing. In this case, the coolant,which flows through the narrowing in accelerated manner, is forced intotwo flows that rotate in opposite directions in the region of thecooling channel ceiling, which flows can interact with the wall of thecooling channel multiple times per piston stroke. In this connection,coolant at a lower temperature is constantly accelerated andadditionally delivered by the narrowing. This effect is particularlyeffective if the radial dimension of the cooling channel ceiling, at itswidest point, is at least equal to twice the radial dimension of thenarrowing. In this case, coolant that is less hot can flow downward, sothat the flow of coolant at a lower temperature through the narrowing isnot significantly hindered.

To optimize this effect, the regions of the cooling channel ceiling thatfollow the flow divider can additionally be configured in arc shape orcircle shape in cross-section. Furthermore, it is particularly practicalto configure the flow divider to be V-shaped or cone-shaped incross-section.

To further optimize the flow conditions in the cooling channel, thecooling channel wall adjacent to the ring belt can be configured to bevertical or inclined at a slant inward.

Another preferred embodiment of the present invention consists in thatthe narrowing is formed by precisely two material elevations, axiallyoffset relative to one another, on two cooling channel walls. Thisembodiment leads to the result that an outer widening is formed in theregion of the cooling channel ceiling, adjacent to the ring belt and/orto the top land, and an inner widening is formed in the region of thecooling channel floor, oriented relative to the piston crown center,particularly adjacent to a combustion bowl that might be present. Inthis way, these regions of the piston head, which are under particularlygreat thermal stress, are very effectively cooled.

In this embodiment, the cooling effect can be influenced, for example,in that the two material elevations have a different thickness, so thatthe two widenings are configured with differently large radii. Thewidening having the greater radius can then be disposed in the region ofthe greatest thermal stress of the piston head.

The present invention is suitable for all piston types and all pistonconstructions, and can be implemented with every piston material.

Exemplary embodiments of the present invention will be explained ingreater detail below, using the attached drawings. These show, in aschematic representation, not true to scale:

FIG. 1 a first exemplary embodiment of a piston according to theinvention, in a partial representation, in section;

FIG. 2 a further exemplary embodiment of a piston according to theinvention, in a perspective partial representation, in section;

FIG. 3 a further exemplary embodiment of a piston according to theinvention, in a partial representation, in section.

FIG. 1 shows a first exemplary embodiment of a piston 10 according tothe invention. The piston 10 can be a one-part or multi-part piston. Thepiston 10 can be produced from a steel material and/or a light-metalmaterial. FIG. 1 shows a one-part piston head 11 of a piston 10according to the invention, as an example. The piston head 11 has apiston crown 12 having a combustion bowl 13, a circumferential top land14, and a ring belt 15 for accommodating piston rings (not shown). Acircumferential cooling channel 16 having a cooling channel floor 17 anda cooling channel ceiling 18 is provided at the level of the ring belt15. The piston 10 furthermore has a piston skirt, in known manner, whichcan be configured in one piece with the piston head 11 or as a separatecomponent, and is connected with the piston head 11 firmly, in knownmanner, or in the manner of an articulated piston, for example (notshown). In this exemplary embodiment of the present invention, thecooling channel 16 has a circumferential narrowing 20. In this exemplaryembodiment, the narrowing 20 is formed by precisely one materialelevation 21 in the cooling channel wall adjacent to the combustion bowl13. In this exemplary embodiment, the cooling channel wall 22 adjacentto the ring belt 15 is configured to be essentially vertical. It canalso be configured to be inclined at a slight slant inward, i.e. in thedirection of the combustion bowl 13.

The cooling channel ceiling 18 of the cooling channel 16 is configuredessentially in dome shape. In this exemplary embodiment, the narrowing20 has essentially the same distance A from the cooling channel floor 17and from the cooling channel ceiling 18 at its narrowest point. In theend result, the coolant is forced into a flow that circulates in acircle, in the region of the cooling channel ceiling 18, as indicated bythe circular arrows, so that the coolant can interact with the wall ofthe cooling channel, in the region of the piston crown 12 and of thecombustion bowl 13, multiple times per piston stroke. In thisconnection, coolant at a lower temperature is constantly accelerated andadditionally delivered through the narrowing 20. To optimize thiseffect, in this exemplary embodiment the radial dimension B of theessentially dome-shaped cooling channel ceiling 18, at its widest point,is at least equal to twice the radial dimension b of the narrowing 20,in other words B≧2×b. In this case, coolant that is less hot can flowdownward, so that the flow of coolant at a lower temperature through thenarrowing 20, in the direction of the cooling channel ceiling 18, is notsignificantly hindered.

The piston 10 or the upper piston part 11 according to the invention canbe produced, in known manner, by means of casting, forging, sintering,etc. In a one-piece upper piston part 11 as shown in FIG. 1, the coolingchannel configured according to the invention can be produced, in knownmanner, by means of casting with a salt core.

FIG. 2 shows a further exemplary embodiment of a piston 110 according tothe invention. The piston 110 can be a one-part or multi-part piston.The piston 110 can be produced from a steel material and/or alight-metal material. FIG. 2 shows a one-part piston head 111 of apiston 110 according to the invention, as an example. The piston head111 has a piston crown 112 having a combustion bowl 113, acircumferential top land 114, and a ring belt 115 for accommodatingpiston rings (not shown). A circumferential cooling channel 116 having acooling channel floor 117 and a cooling channel ceiling 118 is providedat the level of the ring belt 115. The piston 110 furthermore has apiston skirt, in known manner, which can be configured in one piece withthe piston head 111 or as a separate component, and is connected withthe piston head 111 firmly, in known manner, or in the manner of anarticulated piston, for example (not shown).

In this exemplary embodiment of the present invention, the coolingchannel 116 has a circumferential narrowing 120. In this exemplaryembodiment, the narrowing 120 is formed by precisely two materialelevations 121, which lie opposite one another, in the two coolingchannel walls adjacent to the combustion bowl 113 and the ring belt 115,respectively.

In this exemplary embodiment, the cooling channel ceiling 118 of thecooling channel 116 has a flow divider 123 at its zenith, which divideris disposed centered relative to the narrowing 120. In this exemplaryembodiment, the distance of the narrowing 120 from the cooling channelfloor 117 is approximately precisely as great as the distance of thenarrowing 120 from the cooling channel ceiling 118. In the end result,the coolant that flows through the narrowing 120, in accelerated manner,is forced into two flows that rotate in opposite directions, in theregion of the cooling channel ceiling 118, as indicated by the circulararrows that run in opposite directions, so that the coolant can interactwith the wall of the cooling channel 116, in the region of the pistoncrown 112 and of the combustion bowl 113, multiple times per pistonstroke. In this connection, coolant at a lower temperature is constantlyaccelerated and additionally delivered through the narrowing 120. Tooptimize this effect, in this exemplary embodiment the radial dimensionB of the cooling channel ceiling 118, at its widest point, is at leastequal to twice the radial dimension b of the narrowing 120, in otherwords B≧2×b. In this case, coolant that is less hot can flow downward,so that the flow of coolant at a lower temperature through the narrowing120, in the direction of the cooling channel ceiling 118, is notsignificantly hindered.

To optimize this effect, in this exemplary embodiment the regions 118 a,118 b of the cooling channel ceiling 118 that follow the flow divider123 are configured to be arc-shaped or circular in cross-section, andthe flow divider 123 is configured to be V-shaped in cross-section.

The piston 110 or the upper piston part 111 according to the inventioncan be produced, in known manner, by means of casting, forging,sintering, etc. In a one-piece upper piston part 111 as shown in FIG. 2,the cooling channel 116 configured according to the invention can beproduced, in known manner, by means of casting with a salt core. If theupper piston part 111 is configured in two parts and the two parts areconnected with one another by means of friction welding, thefriction-welding seam can be laid through the cooling channel 116, sothat material elevations 121 that lie opposite one another and bringabout the narrowing 120 can be formed by friction-welding beads, as theyoccur, in known manner, during the friction-welding process.

FIG. 3 shows a further exemplary embodiment of a piston 210 according tothe invention. The piston 210 can be a one-part or multi-part piston.The piston 210 can be produced from a steel material and/or alight-metal material. FIG. 3 shows a one-part piston head 211 of apiston 210 according to the invention, as an example. The piston head211 has a piston crown 212 having a combustion bowl 213, acircumferential top land 214, and a ring belt 215 for accommodatingpiston rings (not shown). A circumferential cooling channel 216 having acooling channel floor 217 and a cooling channel ceiling 218 is providedat the level of the ring belt 215. The piston 210 furthermore has apiston skirt, in known manner, which can be configured in one piece withthe piston head 211 or as a separate component, and is connected withthe piston head 211 firmly, in known manner, or in the manner of anarticulated piston, for example (not shown).

In this exemplary embodiment of the present invention, the coolingchannel 216 has a circumferential narrowing 220. In this exemplaryembodiment, the narrowing 220 is formed by precisely two materialelevations 221 a, 221 b, disposed axially offset from one another, inthe two cooling channel walls adjacent to the combustion bowl 213 andthe ring belt 215, respectively. As a result, an inner widening 224 thatextends to the combustion bowl 213 is formed in the region of thecooling channel floor 217. Furthermore, an outer widening 225 thatextends to the uppermost ring groove of the ring belt 215 and to the topland 214 is formed in the region of the cooling channel ceiling 218.This leads to the result that in engine operation, these regions of thepiston head 211, which are under particularly great thermal stress,namely the piston crown 212 in the region of the combustion bowl 213 andof the top land 214, are cooled very effectively. This cooling effect isalso influenced, in this exemplary embodiment, in that the materialelevation 221 a has a thickness D1 that is greater than the thickness D2of the material elevation 221 b. Consequently, the inner widening 224has a greater radius than the outer widening 225. Accordingly, theregion of the combustion bowl is cooled particularly effectively duringengine operation. Of course, the material elevation 221 b can also havea greater thickness than the material elevation 221 a, so that in thiscase, the outer widening 225 has a greater radius than the innerwidening 224, and consequently the region of the piston crown 213 and ofthe top land 214 is cooled particularly effectively (not shown).

Within the scope of what is possible in terms of design, the widenings224, 225 can extend to any desired degree in the radial direction,inward or outward, respectively, as indicated with a dot-dash line inFIG. 3.

The cooling channel floor 217 and the cooling channel ceiling 218 of thecooling channel 216 are configured essentially in dome shape. In thisexemplary embodiment, the narrowing 220, at its narrowest point, hasessentially the same distance A from the cooling channel floor 217 andfrom the cooling channel ceiling 218. In the end result, the coolant isforced into a flow that circulates in circle shape, counterclockwise, inthe region of the cooling channel floor 217 and in the region of thecooling channel ceiling 218, as indicated by the circular arrows. Thus,the coolant can interact with the wall of the cooling channel, in theregion of the piston crown 212 and of the combustion bowl 213, multipletimes per piston stroke. In this connection, coolant at a lowertemperature is constantly accelerated and additionally delivered throughthe narrowing 220. To optimize this effect, in this exemplary embodimentthe radial dimension B of the inner widening 224 and of the outerwidening 225, respectively, at its widest point, in each instance, is atleast equal to twice the radial dimension b of the narrowing 20, inother words B≧2×b, as shown in FIG. 1 using the example of the outerwidening 225. In this case, coolant that is less hot can flow downward,so that the flow of coolant at a lower temperature through the narrowing220, in the direction of the cooling channel ceiling 218, is notsignificantly hindered. Because, at the same time, part of the freshcoolant at a lower temperature circulates in a circular flow in theregion of the cooling channel floor, instead of flowing upward throughthe narrowing 220, whereby this coolant is not excessively heated by hotcoolant flowing back out of the region of the cooling channel ceiling218, the region of the combustion bowl is also effectively cooled.

The piston 210 or the upper piston part 211 according to the inventioncan be produced, in known manner, by means of casting, forging,sintering, etc. In a one-piece upper piston part 211 as shown in FIG. 3,the cooling channel 216 configured according to the invention can beproduced, in known manner, by means of casting with a salt core.

1. Piston (10, 110, 210) for an internal combustion engine, having apiston head (11, 111, 211) and a piston skirt, wherein the piston head(11, 111, 211) has a circumferential ring belt (15, 115, 215) as well asa circumferential cooling channel (16, 116, 216) in the region of thering belt (15, 115, 215), having a cooling channel floor (17, 117, 217)and a cooling channel ceiling (18, 118, 218), wherein the coolingchannel (16, 116, 216) has a narrowing (20, 120, 220).
 2. Pistonaccording to claim 1, wherein the narrowing (20, 120, 220) has adistance from the cooling channel floor (17, 117, 217) that correspondsto at least one-third of the axial height of the cooling channel (20,120, 220).
 3. Piston according to claim 1, wherein the narrowing (20,120, 220) has a distance from the cooling channel floor (17, 117, 217)that corresponds to at most two-thirds of the axial height of thecooling channel (20, 120, 220).
 4. Piston according to claim 1, whereinthe narrowing (20, 120, 220) has essentially the same distance (A) fromthe cooling channel floor (17, 117, 217) and from the cooling channelceiling (18, 118, 218).
 5. Piston according to claim 1, wherein thenarrowing (20, 120, 220) is configured as a circumferential narrowing(20, 120, 220).
 6. Piston according to claim 1, wherein the narrowing(20, 120, 220) is formed by precisely one material elevation (21) on acooling channel wall, and wherein the cooling channel ceiling (18) isconfigured essentially in dome shape.
 7. Piston according to claim 6,wherein the radial dimension (B) of the essentially dome-shaped coolingchannel ceiling (18), at its widest point, is at least equal to twicethe radial dimension (b) of the narrowing (20).
 8. Piston according toclaim 6, wherein the cooling channel (16) has a cooling channel wall(22) adjacent to the ring belt (15), which is configured to be verticalor inclined at a slant inward.
 9. Piston according to claim 1, whereinthe narrowing (120) is formed by precisely two material elevations (121)that lie opposite one another on two cooling channel walls.
 10. Pistonaccording to claim 8, wherein the cooling channel ceiling (118) has aflow divider (123) at its zenith, which divider is disposed centeredrelative to the narrowing (120).
 11. Piston according to claim 9,wherein the regions (118 a, 118 b) of the cooling channel ceiling (118)that follow the flow divider (123) are configured to be arc-shaped orcircular in cross-section.
 12. Piston according to claim 9, wherein theflow divider (123) is configured to be V-shaped or conical incross-section.
 13. Piston according to claim 8, wherein the radialdimension (B) of the cooling channel ceiling (118), at its widest point,is at least equal to twice the radial dimension (b) of the narrowing(120).
 14. Piston according to claim 1, wherein the narrowing (220) isformed by precisely two material elevations (221 a, 221 b), disposedaxially offset relative to one another on two cooling channel walls. 15.Piston according to claim 14, wherein the two material elevations (221a, 221 b) have a different thickness.